Dem. 676-Nylon Rope (2) E.~perinleulde~'elapef1bu E ~ I ~ ZH.I ICooper. To sho~c: Formation of nylon strand and twisted thread. Materials: Soh. A: 5 g hexane-diamine (hexamethylene-diamine) 95 ml water. Soln. B: 5 g 95 ml cyclohexane. Device H-3, adipic chloride tweezers, medicine dropper, 13 X 100 mm test tube. 30 g. weight; 100 g weight, GOO ml beaker.
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Procedure: Project 5 ml Soln. A in culture tube. To it add 5 ml Soln. B from a medicine dropper with its tip immersed in Soln. A . Insert tweezers, pull out nylon thread. As it emerges, the fiber spreads inside the culture tube, becoming visible. Wind the fiber on a test tube, or have a student walk across the room with it as the thread emerges from the culture tube. Wash the fiber with water and dry it. Finally, twist several strands together to form thread. Try to lift 30 g and 100 g weights with the two different samples. Observations: The formation of the fiber in the culture tube projects beautifully. The 100 g weight breaks the single strand, but not the twisted strand; the single strand will support the 30 g weight. Reference:
WITTBECKER, E. L., KINSINGER, J. B., Chent. and Eng.
and MORGAN, P. w., News, Sept. 15, 1958,
page 52.
Procedure: Project C-2 with cell half full of AsCla-aq. Add Xn2S-nq dropwise. Using syringe, t,ransfer the product to the filter paper. Finally remove paper aud exhibit. Obseruations: A henvy precipitate of As& is caught on t,hc paper; yellow (may be opaque) AszS3-sol runs t,hrough t,he paper.
2. DIFFUSION IN GELATIN
Dem 679-Diffusion of H+ versus Fe+++ (I) To show: The relative rates of diffusion of Fe+++ and H + in a gelatin film.
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Materials: Solution containing 2 g IGFe(CN)e 100 ml H 2 0 5 drops phenolphthalein indicator solution 1 drop NaOH. Soak three gelatin strips (SD-4) in this solution and dry; FeCla-aq.
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Procedure: Put a large drop of FeC13-aq in the center of each strip (a) three hours before (b) one hour before and (c) immediately before projection. Project all three strips simultaneously. Observations: (a) all blue. (b) Red, white and hlue. (c) All red. These results can he explained as follows. As the H + diffuses it decolorizes the red (phenolphthaOH-). As the Fe+++ diffuses i t forms blue lein ferric ferrocyanide. The H + diffuses faster than the Fe+++.
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23. COLLOIDS
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A. Types of Colloids
Dem. 680-Diffusion of H+ Fe+++ (2) Experiment developed by W. H. Slabaugh.
B. Relative Size of Particles 1. FILTERABILITY
Dem. 677-Mud, vs Cu++ vs Fe(OH)3-Sol To show: Ability of various particles to pass bhrough filter paper. 0
Materials: CuCI2-aq, mud, C-3, f&nels, filter paper. Fe(OH)3-sol made by boiling dilute FeC13-aq for 1 min to dark red. Proceclure: Fit filter paper to the 3 funnels, insert in C-3 and project. Pour CuClz-aq, muddy water, and Fe(OH)a-sol through the paper. Also show papers to class. Obselvations: Some mud particles are too large to pass through the paper, Cu++ ions, Fe(OH)3-sol, and colloidal mud particles all pass through.
Dem. 678-As& Precipitate versus A&-Sol To fihot~': Format,ion of hoth precipitate and sol in forming As&. Materials: Very dilute Na3-aq and AsC13-aq (Asz03in HClj; C-2, syringe, funnel with filter paper. A756 /
Journal o f Chemical Education
To show The relative rates of diffusion of Fe+++ and H + in a tube of gelatin. Materials: Agar-agar, FeCkaq, NaOH-aq, IWe(CA')6-aq, phenolphthalein indicator. Procedure: Dissolve 1 g agar-agar in 100 ml water by boiling. Row stir in 1 drop phenolphthalein indicator 1 drop NaOH-aq (to pink). Three-quarters fill three culture tubes with this solution. Let stand until gelled. Cover each with H 2 0 containing 1drop FeClraq 24 hr, 2 hr, and just before lecture. Project all three tubes in H-3.
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Observations: I n tube 1 three bands of equal width form; red, the original material; white, where the H + ion has diffused 2/3rds the way into the agar (about an inch) and neutralized the OH- to turn the indicator colorless; and blue, where the Fe+++has diffused onethird the way into the agar to form Prussian Blue, ferric ferrocyanide. I n tube 2 diffusion has just commenced, with half an inch band of white and half an inch band of hlue. I n tube 3 diffusionhas not begun. Note 1. Gelatin is too acid for this experiment, therefore agar-agar is used. 2. Actually the H+ is hydrated, e.g. as H30+
